Omfg
http://www.exrx.net/Muscles/PectoralisSternal.htmlSternal head is low/central part
Clavicular head is the upper part;
and you have a minor.
It's one big muscle, they'll react/contract at the same time,
you can put more focus on a part, but it's one muscle.
So if you're gonna do incline press, you put more focus on the clavicular head, but your minor will also react/contract. The same for decline,
you put more focus on the minor, but clavicular will also react/contract.
And you cannot train a musclefiber at a certain point (left/right- in- outside) more. The fiber contracts at once, and relaxes at once. It's nature.
The only thing that is possible is to try to achieve a maximum ROM.
With dumbellpress you can achieve a greater ROM that with barbell-press. Cables insures a maximum load during the exercise,
with dumbells and or barbell you have a dead point at a certain point, with cables this dead point is reduced significantly.